1. Field of the Invention
This invention relates to rotary cone rock bits of the type that operate in hydraulic fluid or "mud".
More particularly, this invention relates to three cone rock bits having easily interchangeable, partially extended hydraulic nozzles protruding from two of the three 120.degree. leg segments that comprise the body of the rock bit. The third 120.degree. leg segment is devoid of a nozzle, hence fluid exiting from the two mini-extended nozzles will cross the cutting face of the bit, sweeping detritus from the borehole bottom and up the previously drilled borehole shaft.
2. Description of the Prior Art
There is much prior art that deals with fluid flow through a rock bit. One of the major problem areas in rock bit penetration is the removal of formation cuttings from a borehole so that the cutting end of the bit attacks new formation and not old cuttings.
Conventional nozzles generally lack sufficient flow velocity or hydraulic power to sweep the hole bottom of detritus. Fluid from conventional nozzles, released adjacent to the dome area of a rotary cone rock bit, entraps detritus-laden fluid near the dome and forces the cuttings back under the cones where they are reground, thus inhibiting the penetration rate of the rock bit during drilling operations.
The following patents all teach the use of higher fluid flow velocities to enhance rotary cone drill bit operations.
U.S. Pat. No. 2,815,936 utilizes a pair of oppositely opposed nozzles extending from a dome area formed by the bit body to direct fluid between the pair of cones and against the borehole bottom. A pair of low velocity nozzles are directed at the cutter cones to clean the debris from the cutting surface.
U.S. Pat. Nos. 3,363,706 and 3,509,952 both teach extended nozzles, emanating from the dome area, having their exit plane just above the borehole bottom. Three extended nozzles pass between three cutter cones to direct fluid at the borehole bottom.
U.S. Pat. No. 4,106,577 combines a centrally positioned high pressure water jet drill with rotary cutter cones to facilitate formation penetration. Multiple apertures in the end of the injector head of the central jet direct fluid in different directions to enhance bit penetration.
The foregoing patents, while they attempt to more efficiently utilize hydraulic action to enhance formation drilling, fail to remove the detritus from the borehole bottom in an expeditious manner, resulting in regrinding of the cuttings before they can be moved from the borehole bottom.
U.S. Pat. Nos. 4,126,194; 4,187,921 and 4,189,014 are assigned to the same assignee as the present invention. These patents generally teach sweeping the bottom of a formation to remove detritus therefrom. The '194 patent teaches the use of two nozzles, one each in 120.degree. leg segments, the third 120.degree. leg segment having a funnel-type pickup tube axially aligned with the rock bit body, an inlet end of the tube being positioned just above the borehole bottom. The idea is to sweep formation cuttings across the borehole bottom and up the pickup tube. While this invention has considerable merit, the pickup tube lacks sufficient size to handle a large volume of cuttings.
The '921 patent utilizes opposed extended nozzles in a two rotary cone rock bit. Crossflow of hydraulic fluid is generated by cavitating one of the two opposed nozzles. The pressure differential between the two nozzles encourages crossflow, thereby sweeping the borehole bottom during rock bit operation.
The '014 patent was designed to enhance crossflow of drilling fluid. Two nozzles, one each in 120.degree. leg segments, are mounted slightly extended from the dome portion of the bit. Each nozzle is sealed on the gage side of the 120.degree. leg segment to assure crossflow of fluid toward the remaining, nozzleless 120.degree. leg segment. The last mentioned segment is open to the borehole annulus for passage of rock bit cuttings. A flow diverter is mounted in the center of the dome to decrease the dome area, thereby increasing the flow velocity around the diverter and across the bit face. The diverter also serves to discourage the accumulation of formation cuttings that tend to "ball up" in the center of the bit.
The present invention is a vast improvement over the '014 patent in that flow velocities are increased dramatically and flow patterns are established around the cutter cones to ensure expeditious removal of detritus away from the cutting end of the rock bit, thereby obviating the need of a dome flow diverter and "sealed" nozzle area during operation of the bit in an earthen formation.
Finally, U.S. Pat. Nos. 4,369,849 and 4,516,642 attempt to direct fluid flow in such a manner as to move detritus from the borehole bottom. The '849 patent utilizes multiple nozzles at various angles with respect to the axis of the rock bit. The nozzles are also positioned in the dome area in a spiral pattern. The spiral nozzle configuration attempts to create a spiral flow path of fluid on the borehole bottom.
The '642 patent teaches directing a stream of fluid through a nozzle at the leading cutting edge of a rotary cutter cone to both clean the teeth of the cone and to move cuttings away from the advancing roller cone. In a multiple cone bit, each cone has its own nozzle. The nozzle is canted or angled toward the leading edge of the rotary cone to clean the cutting elements extending from the cone surface. The cuttings, however, tend to circulate on bottom due to the nozzles being circumferentially symmetrically spaced around the rock bit body where three cone bits are utilized.
Borehole cuttings tend to adhere or "stick" to the bottom of a borehole due to hydraulic pressures from the drilling fluid being pumped down the drillstring from the floor of the drilling rig. It requires a great deal of agitation to force the detritus adhering to the borehole bottom up the annulus formed between the drillstring and the borehole to prevent the cutting end of a drill bit from regrinding or recutting this debris.
The present invention is primarily directed to accelerate the removal of detritus from the bottom of a borehole, thereby enhancing rock bit penetration.
The use of mini-extended nozzles with special nozzle profiles to accelerate hydraulic fluid therethrough and a nozzleless 120.degree. leg segment to create crossflow of fluid over the borehole bottom assures removal of borehole cuttings therefrom.
A centerjet, which employs either a converging or diverging internal flow passage, may be employed to further encourage removal of detritus during drilling operations.